In cystic fibrosis several functions of airway epithelia are abnormal, and deficiencies in both Cl.sup.- transport and Na.sup.+ absorption are well documented. See, e.g. Knowles et al., Science 221, 1067 (1983); Knowles et al., J. Clin. Invest. 71, 1410 (1983). It is believed that impaired chloride secretion is one of the causes of the thickened airway surface liquid that characterizes cystic fibrosis. This thickened airway fluid contributes to the recurrent pulmonary infections and loss of ventilatory function that occur in cystic fibrosis. Retained airway secretions are also known to contribute to the morbidity of other pulmonary diseases such as asthma and chronic obstructive pulmonary disease.
The therapeutic goal in cystic fibrosis and other pulmonary diseases in which the water content of the mucus is altered is to remove retained secretions from the lungs. For example, the use of aerosolized amiloride to facilitate the removal of retained mucus secretions is described in U.S. Pat. No. 4,501,729. Amiloride appears to block Na.sup.+ reabsorption by airway epithelial cells, and therefore inhibits water absorption from mucus.
A different therapeutic approach is to increase the water content of the airway surface liquid by modulating the activity of chloride channels. An example of this is the administration of ATP or UTP, which appear to induce hydrated mucus secretions by stimulating chloride secretion from respiratory epithelial cells. See, e.g., C. Stock, Breathing Easier: A Promising Treatment for Cystic Fibrosis, Endeavors, 10, 10-11 (Fall 1992) (Published by the Office of Research Services, The University of North Carolina at Chapel Hill).
Tuberculosis, while also primarily involving the lungs of afflicted subjects, is an infectious disease caused by the bacteria Mycobacterium tuberculosis. While most commonly occurring in the lungs, tuberculosis infections may occur anywhere in the body and may be widely disseminated. The development of streptomycin in 1944, isoniazid (INH) in 1952, ethambutol in 1952, and rifampin in 1972 led to a decreasing prevalence of tuberculosis up until approximately 1985, when the number of reported cases began to increase, Bloom and Murray Science, 257, 1055 (1992). Outbreaks of multi-drug resistant (MDR) tuberculosis are occurring with increasing frequency, and pose a major public health problem, Morbidity and Mortality Weekly Report, 41, 5 (1992). Tuberculosis remains the leading cause of death in the world from a single infectious disease.